Advanced consumer electronics such as miniature radios and wristwatch cellular phones pose severe limitations on the size and cost of frequency selective units (e.g., frequency references and filters) contained therein. MEMS (micro-electro-mechanical systems) resonators are receiving increased attention as building blocks for integrated filters and frequency references to replace bulky, off-chip ceramic and SAW (surface acoustic wave) devices, among others. Small size, low power consumption and ease of integration with microelectronic circuits constitute some major advantages associated with the use of MEMS resonators.
To achieve the desired frequency selectivity, high-order bandpass filters consisting of a plurality of mechanically-coupled resonators are typically used. Mechanical coupling techniques, traditionally used for implementation of high-order filters from individual mechanical resonators, have been applied to micromechanical resonators for filter synthesis. Electrostatically sensed and actuated MEMS filters up to the third order with center frequencies up to 68 mega-Hertz (MHz) as well as electrostatically actuated and optically sensed filters up to the 20th order at center frequencies of a few MHz have been reported using mechanical coupling techniques.
Mechanical coupling techniques can present obstacles to performance in some applications. For example, in the ultra-high frequency (UHF) range (e.g., 0.3–3 giga-Hertz (GHz)) and above, which is a band of interest for many wireless applications, due to the very small size of the resonator element (approximately less than 10 micro-meters (μm)), mechanical coupling may require sub-micron in size coupling elements (e.g., wires) that are difficult to fabricate using optical lithography. In addition, filter characteristics are largely dependent on the positioning and/or dimensions of the coupling elements and optimized design of a filter often requires mechanical design expertise and/or specialized simulation tools.
Thus, a need exists in the industry to address the aforementioned and/or other deficiencies and/or inadequacies.